Motor-driven toothbrushes have been proposed and marketed commercially for many years, especially since long-lived rechargeable batteries and miniature electric motors have been available. A common form of motor-driven toothbrush comprises a hand-holdable drive unit and a brush unit that is pivoted about its axis relative to the drive unit by a motor-driven transmission, and thereby pivots the brushes as a unit from side-to-side so that they brush generally up and down on the teeth. In another known form a brush unit is reciprocated axially by a drive unit such that the brush moves generally from side to side across the teeth. A motor-driven toothbrush that allows the user to switch between a side-to-side pivot motion and an axial reciprocating motion of the brush head is currently being marketed. Also available is a motor-driven toothbrush in which a single, relatively large tuft of bristles is rotated unidirectionally about an axis parallel to the bristles in a manner similar to that of a cleaning brush used in a dentist's drill head by dental hygienists in cleaning teeth.
The motor driven toothbrush described and shown in U.S. Pat. No. 4,156,620 (Clemens, May 29, 1979) has a brush head carrying several bristle tufts, each of which is mounted to rotate about its lengthwise axis on a tiny spindle having a pinion gear. The bristle tufts are arranged in two ranks, one on each side of the longitudinal axis of the brush head, and the gears of the spindles of each rank mesh to form a train. Every other spindle in each rank is offset laterally from the remaining spindles. A motor in a hand-holdable drive unit drives through a gear transmission a crank arm that is linked to a longitudinally movable drive shaft extending through the brush head and having a rack gear on its end portion that meshes with the pinion gears on alternate ones of the bristle-mounting spindles in each rank. As the drive shaft reciprocates, the driven bristle tufts are rotated, first in one direction and then the other. The remaining bristle tufts are rotated in opposite directions to the driven ones due to the intermeshing of the gears in each rank. A motor-driven toothbrush of the type described and shown in the Clemens patent is widely sold.
Previously known motor-driven toothbrushes of the type in which the entire brush unit is moved relative to the drive unit in either rotational or axial reciprocation have several disadvantages. The bristle tufts, which are arranged in crosswise and lengthwise rows, move along straight tracks either up and down or crosswise over the teeth with gaps between the tracks. Therefore, thorough cleaning requires that the user move the device over the teeth to cover all areas, lest areas of the teeth not be cleaned where the gaps between the tuft rows are. The reactive forces to the brush movements are transmitted to the drive unit and by the brush unit to the user's hand, and some people do not like the vibration felt by the hand. Similarly, the back of the brush head often contacts and vibrates the lips and the tissues in the mouth, which can also be unpleasant for some users. The longitudinally reciprocating types of brushes move exclusively across the teeth, and the bristles tend to move past the spaces between the teeth. Massaging of the gums is important to good dental hygiene, but the solely linear movements of the bristles do not produce a thorough massaging action for stimulation of blood circulation and tissue toning.
As far as cleaning the teeth is concerned, the individual rotating tufts of the Clemens patent type toothbrush do an excellent job. Because the individual tufts move very little transversely relative to their axes, however, the gum-massaging action is limited. The single rotating bristle tuft toothbrush requires considerable attention by the user to full coverage of the teeth and also fails to massage the gum tissues effectively.